Process of producing non-fibrillating acrylonitrile polymer filaments with wet steamtreatment and products produced thereby



United States Patent I 2,926,934 1 11061555 or PRODUCING NON-FIBRILLATING ACRYLONITRILE POLYMER FILAMENTS WITH W ET STEAM TREATMENT AND PRODUCTS PRODUCED THEREBY Rodger L. Schaefer, Edward H. Sundbeck, and Roy W. sudholf, Decatur, Ala., assignors to The Chemstrand V Corporation, Decatur, Ala., a corporation of Delaware No Drawing. Application December 19, 1955 Serial No. 553,714

14 Claims. (Cl. 8-1301) This invention relates to new and improved acryloniproved structuresformed from blends of the acrylonitrile polymers with other polymers formed from polymerizable monoolefinic monomers.

By structures, as employed throughout the instant specification and claims, is meant fibers, filaments, bundles of filaments, yarns, threads, foils, ribbons, films, and the like. However, for the sake of simplicity of description, the present invention will be described as it is applicable to the production of filaments, including bundles of filaments and fibers, it being understood that this is merely intended in an illustrative sense and the invention should not be limited thereby, but only insofar as the same may be limited by the appended claims.

Polymers of acrylonitrile containing at least 70% by weight of polymerized acrylonitrile and blends thereof are well-known in the art of synthetic fiber and filament production. In general, the acrylonitrile polymers are quite useful for the production of synthetic fibers and filaments because it is possible to obtain the high tensile strength and other desirable physical properties required in salable fibers and filaments.

Various methods may be employed in producing structures, such as fibers and filaments, from acrylonitrile polymers including the so-called wet spinning process. This process comprises extruding a solution of the acrylonitrile polymer through a spinneret into a bath comprising a liquid which will readily leach out the solvent from the polymer solution and coagulate or precipitate the polymer from its solution, the filaments being carried through the bath for a period of time sufiicient to solidify the polymer to the desired extent. Usually, the filaments are subjected to a stretching operation, preferably while they are in the gel state, in order to increase their tenacity as well as otherwise to improve physical properties by orienting the polymer molecules of which the filaments are composed.

Filaments produced from acrylonitrile polymers by the wet spinning process have excellent physical properties but do sulfer from one serious defect, namely, fibrillation. That is, the fibers and filaments, when formed into yarns and in turn fabrics, split off fibrils when subjected to excessive wear in any given area.

Fibrillation is a phenomenon induced in fibrous materials by the application of stress, usually in the form of abrasion, and is characterized by the splitting off from the parent filament or fiber of longitudinal sections of material which are usually referred to as fibrils. The di- Patented Jan. 12, 1960 e we mensions of the fibrils are small compared to those of the original filament fiber. 'The splitting off of 'the' fibrils is referred to as fiber breakdown and can readily be observed under the microscope, where the presence of fibrils may be seen. In undyed fabrics, however, the presence of fibrils may be unobserved.

Dyed fabrics, formed from filaments and fibers of acrylonitrile polymers by the wet-spinning process, and particularly those fabrics composed of surface-dyed filaments and fibers, readily display the effects of fibrillation. In abrasion causing fibrillation, such as at the wear points of clothing, shade changes will be produced in the area of abrasion due to the exposure of undyed, internal portions of filaments and fibers and/ or the reduced particle size of the fibrils which, through a light-scattering effect, produces an apparent color change. Obviously, such a change in color is to be avoided and so long as filaments and fibers have a tendency to fibrillate, they are practically useless in most commercial applications.

As previously pointed out, the acrylonitrile polymer filaments are stretched in order to orient the molecules therein. The purpose of this procedure is to increase the tenacity of the filaments to a practical point. However,

it has been found that fibrillation occurs in highly-oriented, crystalline filaments which are of such morphological structure that they possess high longitudinal strength and low transverse strength. It was first thought that such fibrillation could be overcome by a reduction in orientation to be accomplished by the use of lower stretch. However, such reduction in the amount of stretch, while overcoming fibrillation to a certain degree, did not produce filaments having the necessary low fibrillation and in addition, the reduction in amount of stretch resulted in a deleterious eifect on other desirable and essential properties in the filaments and fibers, such as reduction in tenacity and elongation, and the like. Accordingly, a continued effort has been made to overcome the objectionable fibrillation without deleteriously affecting the essential and desirable properties of acrylonitrile polymer structures and still produce a salable product.

It is an object of the present invention to provide new and improved acrylonitrile polymer structures which do not fibrillate or which fibrillate to only a negligible degree which in turn does not affect their commercial utility. Another object of the present invention is to provide a new and improved process for the manufacture of non-fibrillating acrylonitrile polymer structures. It is still another object of the instant invention to provide a new and improved wet-spinning process for the manu facture of acrylonitrile polymer fibers and filament. Other objects and advantages of the present invention will in part appear and will in part be apparent from the description thereof hereinafter.

It has unexpectedly been found, and in general, the objects of the present invention are accomplished, that acrylonitrile polymer structures which do not fibrillate, or fibrillate to a negligible degree, can be produced by subjecting the acrylonitrile polymer structure to a high temperature and pressure in the presence of saturated or wet steam. The tow or bundle of filaments is placed in a closed chamber, such as an autoclave, or like pressure apparatus, and the chamber is evacuated. Thereafter wet steam is run into the autoclave until a pressure of 30 to- 60 pounds per square inch is registered therein. Immediately upon reaching the desired pressure, the chamber is vented and again the chamber is evacuated. Then the vacuum in the chamber is broken and the tow removed therefrom and cut into staple fibers, if desired.

The wet steam treating cycle described above may be repeated as many times as desired. In many instances, where a large amount of filaments are being treated at one time, it is necessary to repeat the cycle several timesin order to insure efficient and complete penetration of the steam throughout the entire mass. When employing more than one cycle or repeating the steam treatment, the steam pressure is reduced to around 2 psi. before introducing further steam. It is to be noted that the actual time required to steam treat or anneal a. single filament is a fraction of a second. Thenumber of cycles .pounds of tow were so treated.

When producing filaments and fibers from acry-l'onitrile polymers the finished product is not a true white and many proposals have been made for improving the color of 'the filaments and fibers or rather, reducing thecolor therein. In the present process, such color is reduced when the chamber or autoclave or like equipment is evacuated prior to the introduction of wet steam. It has been found that an initialvacuum of approximately inches reduces color and also insures or assists in the proper steam penetration.

The steam pressure is an important factor in the present invention in order to obtain the desirable results, i.e., in order to obtain the optimum yarn properties, such as strength, elongation, fiber breakdown, fibrillation rating and color. It has been found that when steam pressures below 25 psi. are employed, the resulting filaments and fibers have a fibrillation rating, explained in more detailhereinafter, which is too high. When steam pressures above 60 p.s.i. are employed, the resultant yarn strength is too low and too much color is developed in the filaments and fibers. The optimum results with. respect to fiber properties are obtained when steam pressures in the range of to p.s.i. are employed.

In the practice of the present invention, it is important that the temperature of the steam, when introduced into the closed chamber, be in the range of 135 to 155 C., i.e., steam under a pressure of 30 to psi. Further, the steam must be wet. It is necessary that the acrylonitrile polymer structures be wet with the steam. during treatment. Normally, very high temperatures would be necessary to overcome the internal bonding forces within the structure which are believed to cause fibrillation. However, the presence of a plasticizer, such as water in the form of wet or saturated steam, permits lower temperatures to be employed than would be otherwise possible. standpoint of undesirable color formation in the structure during treatment.

The final vacuum is employed in the instant process in order to cool the filaments or fibers in the chamberv or autoclave, thereby reducing color development in the filaments, and to remove excess water from the tow or bundle of filaments.

The present invention is applicable to. structures formed from various acrylonitrile polymers and blends thereof, for example, polyacrylonitrile, copolymers. and terpolymers of percent or more of acrylonitrile and up to 30 percent of other polymerizable mono-olefinic monomers, such as vinyl acetate and other vinyl esters of monocarbcxylic acids, vinylidene chloride, vinyl chloride and other vinyl halides, dimethyl fumarate and other dialkyl esters of fumaric acid, dimethyl maleate and other dialkyl esters of maleic acid, methyl acrylate and-other alkyl esters of acrylic acid, styrene and other vinyl-substituted aromatic hydrocarbons, methyl. methacrylate and other alkyl esters of methacrylic acid, methacrylonitrile, alpl'iaivinylpyridine and other vinyl-.substitutedfheterocyclienitrogen ring compounds,; such as; the vinyl imidazolesretc thealkyl-substituted vinylpyridines, Sllfihi as: 2,-meth-yl-5-vinylpyridine and the: like, vinyl allyl-.- and:

methallyl,chloroacetatn, alpha-methylstyrene, allyl, glyc-a This is a distinct advantage particularly from the v idyl ether, methallyl glycidyl ether, allyl glycidyl phthalate and the corresponding esters of other aliphatic and aromatic dicarboxylic acids, glycidyl acrylate, glycidyl methacrylate and other mono-olefinic monomers copolymerizable with acrylonitrile. Of particular utility are the comonomers which contain one polymerizable olefinic radical whereby the copolymerization with acrylonitrile may be etfected and oneacidic, basic or otherwise reactive group capable of bonding the dyestuif with which the ultimate structure may be treated.

Many of the more readily available comonomers for polymerization with acrylonitrile, form copolymers which are not reactive with the dyestuifs and may therefore be impossible or difficult to dye by conventional techniques. Accordingly, these non-dyeable fiber-forming copolymers may be blended with polymers or copolymers which are in themselves more dye-receptive by reason of their physi cal structure or by reason of the presence of functional groups which are chemically reactive with the dyestutf,

whereby the dyestuif is permanently bonded to the polymer in a manner which lends resistance to-the usual laundering and dry-cleaning procedures. Suitable blending polymers may be polyvinylpyridine, polymers of alkylsubstituted vinylpyridines, polymers of other alkenyl-substituted N-heterocyclic compounds, the copolymers of the various alkenyl-substituted N-heterocyclic compounds,

and other copolymerizable monomers, particularly acrylonitrile.

Ofv particular utility are the blends of non-dyeable aciylonitrile polymers of good fiber-forming properties for example, polyacrylonitrile or a copolymer of more than percent acrylonitrile and up to 15 percent of vinyl acetate, and a copolymer of vinylpyridine or an alkyl substituted vinylpyridine and acrylonitrile, the said acrylonitrile being present in substantial proportions, for example, a total of 50 to 80 percent acrylonitrile in the blend to provide heat and solvent resistance, and a substantial proportion of the pyridine or derivative thereof to render the blend receptive to acid dyestuffs. Of particular utility are the blends of copolymers of to 98 percent acrylonitrile and 2 to 10 percent vinyl acetate and sufilcient copolymer of 10 to 70 percent acrylonitrile and 30 to 90 percent Z-methyl-S-vinylpyridine to produce a blended composition with a total of 3 to 8 percent by weight of Z-methyl-S-vinylpyridine.

Other compositions suitable for blending with nondyeable acrylonitrile polymers are: the polyamides prepared by condensing an alkylene diamine having up to six carbon atoms and a compound of the group consisting of crotonic acid, acrylic acid, methacrylic acid and the alkyl esters of these acids, wherein the alkyl radical has up to five carbon atoms; the polyamides prepared by condensing N-alkylazadinitriles with formaldehyde; the polyesters prepared by reacting dicarboxylic acids with glycols containing tertiary amino groups; and other polymers containing tertiary amino radicals capable of reacting chemically with the acid dyestuifs.

A further class of useful dye-receptive resins suitable for blending with the non-dye-receptive acrylonitrile polymers are the tertiary amino group containing polymers and copolymers described in the preceding paragraphs which have been reacted with aliphatic halides, for example, butyl bromide, chloracetic acid, methyl chloroacetate, with the esters of oxygen containing sulfur acids, which acids have ionization constants greater than 10"-, for example, methyl sulfate and methyl p-toluenesulfonate and with the various acids, such as sulfuric acid, hydrochloric acid and benzenesulfonic acid. By these reactions blending resins containing amino groups are converted to quaternary or tertiary ammonium salts, which are more dye-receptive than are the corresponding amino groupscontainingresins.

Any of the known acrylonitrile polymer polymerization procedures may be employed in making the polymers for-usein the practice of the present invention. As in.

the preparation of acrylonitrile polymer filaments-and fibers by prior art methods, the physical properties of the polymers are of substantialrimportance. It is desirable that the polymers be uniform with respect to molecular weight, particle size, and chemical composition. Accordingly, the methods for their preparation must be selected so as to induce the uniformity of chemical and physicalproperties. In general, the molecular weight should be in excess of 10,000 and preferably in excess of 25,000, the molecular weights beingdetermined by measuring the viscosity of dilute solutions in the manner well-known in the art.

It has been found that polymers and copolymers of desirable physical properties are those which are prepared by the aqueous suspension technique, wherein the monomers or mixture of monomers are added to an aqueous medium maintained under conditions suitable for a rapid but controlled polymerization. The aqueous medium should contain a water-soluble peroxy catalyst and a dispersing agent which induces the precipitation of a finely divided polymer during the reaction. In order to insure the optimum concentration ofperoxy catalyst and dispersing agent it is frequently desirable to add the catalyst and dispersing agent continuously or intermittently throughout the course of the reaction. The preferred practice involves the charging of the monomers or mixtures of monomers, gradually during the course of the reaction at a uniform rate or ata varying rate which permits the maintenance of the reaction at a constant temperature, for example, the reflux temperature.

The fiber-forming acrylonitrile polymers are prepared by polymerization in the presence of water-soluble peroxide catalysts, such as the alkali metal salts of the various peroxy acids, for example, sodium perborate, sodium percarbonate, and potassium persulfate. Stabilizing or dispersing agents, such as the water-soluble salts of the sulfonated mahogany acids, salts of the formaldehyde condensed naphthalene sulfonic acids, salts of sulfonated alkylbenzenes, salts of triethanolamine, sodium stearate and other salts of carboxylic acids, and mixtures thereof prepared by the saponification of animal and vegetable oils.

Desirable methods for the preparation of acrylonitrile polymers of uniform molecular weight involve the use of regulators, for example, tertiary dodecyl mercaptan, beta-mercaptoethanol, thioglycolic acid, beta-mercaptopropionic acid, and acetaldehyde. The nature of the other monomeric substances being polymerized with the acrylonitrile may determine the type of substance useful as a regulator. For example, in the copolymerization of acrylonitrile with monomers, such as vinyl acetate, methyl methacrylate, and styrene, thioglycolic acid is unusually beneficial. However, in the preparation of copolymers of the basic monomers, such as vinylpyridine; the use of tertiary aliphatic mercaptans will be found to be very effective.

The present invention is applicable to the treatment of filaments and fibers formed by. the so-called dryspinning process, wherein a polymer solution in a volatile organic solvent, such as N,N-dimethylformamide, and the like, is extruded into a heated gaseous atmosphere and the solvent is evaporated leaving a coagulated filament, as well as by the wet spinning process. However, the problem of fibrillation is much more acute in filaments formed by the wet spinning process and accordingly, the invention is described in detail as the same is applicable thereto.

In the wet spinning process, a solution of the polymer in a suitable solvent, such as ethylene carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, and the like, commonly referred to as the dope, is extruded through anorifice or a plurality of orifices in the face of a spinneret which in turn is submerged in a coagulating medium or bath. The bath comprises a non-solvent for the polymer which is also a solvent for, or miscible with, the solvent in the dope. The filament, or filaments, as the case may be, are removed from the coagulating bath and passed through a washing medium where all residual solvent and coagulating liquid are removed therefrom. Water is the preferred washing medium and is usually contained in a bath through which the filaments are passed. In the bath, the washing medium may flow concurrent with or countercurrent to the direction of travel of the filaments therethrough. Washing rolls or like apparatus may also be employed. Thereafter the filaments are dried and steam stretched, if desired. In order to orient the polymer molecules in the filaments, and particularly if no steam stretch is to be given, they are stretched While in the washing bath, or coagulating bath, or inboth. Further, a solvent stretch bath may be employed immediately following the coagulating bath Wherein the polymer molecules in the filaments are oriented. Any solvent or plasticizer for acrylonitrile polymers may be employed in the solvent stretch bath. The concentration of the solvent in the bath will depend upon the chem ical characteristics of the solvent used and the temperature of the bath. Obviously, the concentration must be such that the polymer article passing therethrough will not dissolve therein. Certain solvents may be used in higher concentrations than others. For example, up to percent N,N-dimethylacetamide may be employed. This is unexpected but it has been found that acrylonitrile polymer articles will not dissolve in a pure or 100 percent N,N-dimethylacetamide bath if the article is under tension while therein. Usually, however, a solvent stretch bath containing from 10 to 85 percent solvent by weight, such as amide, and the like, is satisfactory.

As previously pointed out, the filaments produced in accordance with the preceding wet spinning procedure, and other similar and conventional wet-spinning procedures, will fibrillate to a very undesirable extent when subjected to abrasion or normal wear in the form of yarns and fabrics. When these filaments are treated in accordance with the present invention, they are substantially non-fibrillating or the degree or amount of fibrillation of the filaments is reduced to a point Where it becomes a matter of insignificance commercially. This is entirely unexpected and the instant invention provides the answer to a magnanimous problem which has plagued the art for a long time.

In the present invention, the fibrillation measurement of a filament or fiber is comparative and such measurement is made on a fabric formed from the filaments or fibers. The degree of fibrillation of a fiber or filament is determined on a tricot knit tape and the value obtained is called a tricot rating or TR. In all of the specific examples set out hereinafter, the tricot tapes were prepared by spinning approximately six ounces of 16 singles yarn with a twist of 14 turns per inch and then knitting 24 inches of tape on a 14 guage machine with 14 ends in each of the front and back warps. All of the tapes were dyed for one hour at the boil with 2% acetate dye (Eastman Blue GLT). After rinsing and centrifuging or blotting, the tapes were pressed with a steam iron and further dried at 60-70 C. Thereafter the tape is flex abraded for cycles on a Stoll abrader or Universal wear tester manufactured by Custom Scientific Instruments, Inc., of Arlington, N. I., using the flexing bar with a 2 lb. tension and /2 lb. weight on the head. Two such abrasions are made on each tape.

Measurement of the loss in depth of shades was made with a Photoelectric reflection meter manufactured by the Photovolt Corporation of New York City. Using the green filter, supplied with the instrument, the instrument is first adjusted to read the 72.5% reflectance of a standard porcelain plate, which is also supplied with the instrument. A blue tape, prepared as outlined above, is selected as a secondary standard with a reflectance in the range of 8-1-2%. The exact reflectance is then measured.

N,N-dimethylacetamide, N,N-d imethylform- '7 The abraded tape is evaluated by taking two measurements of the reflectance of the unabraded portion and one measurement on each of the abraded portions. The average of the former measurements is subtracted from the average of the latter to give the fibrillation or tricot rating (TR). Therefore, this rating (TR) is the difference of the percent reflectance of the abraded and unabraded portions of the tape.

The ultimate in TR rating would be zero. However, from a commercial standpoint and for all practical purposes, a TR of 1.0-2.0 indicates a filament or fiber which is substantially non-fibrillating. Heretofore, acrylonitrile polymer structures have had a TR rating in the range of about 3.0 to 10.0. Filaments and fibers for certain specific applications in the trade, where fibrillation is not of critical importance, have been acceptable with a TR rating of -6. However, the commercial application of such filaments and fibers has been definitely limited and a great desire in the art has existed for filaments and fibers which are substantially non-fibrillating or which have a TR rating of at least as low as 2.0 and preferably lower. This long felt Want in the art has been accomplished by the present invention.

For a more detailed description of the present invention, reference should be had to the following specific examples which are merely intended in an illustrative sense and are not intended to be limitative. In the examples, all parts and percents are by weight unless otherwise indicated.

EXAMPLE I In this example a polymer blend was employed. A copolymer (A) was made containing 94% by weight of acrylonitrile in the polymer molecule and 6% by weight of vinyl acetate. A second copolymer (B) was made containing 50% by weight of acrylonitrile in the polymer molecule and 50% by weight of Z-methyl-S-vinylpyridine. Thereafter, a sufiicient amount of copolymer (B) was blended with copolymer (A) to give 6% by weight, based on the weight of the blend, of 2-methyl-5-vinylpyridine in the blend. The polymer blend was then dissolved in N,N-dimethylacetamide to form a spinning solution or dope containing 18% solids. The dope was extruded through a spinneret which was submerged in a coagulating bath containing 50% N,N-dimethylacetamide and 50% water. The orifices in the face of the spinneret were of such size as to give a filament having a final denier of 3. The filaments were removed from the coagulating bath and washed continously with water at a temperature of approximately 100 C. Thereafter the filaments were dried by passing over heated rollers. The dried filaments were cut into staple fibers by means of a cutter. One hundred (100) pounds of the staple fibers were placed in a perforated metal container which in turn was placed in an autoclave. The autoclave was evacuated and saturated steam at approximately 40 p.s.i.g. was introduced into the autoclave until the pressure therein reached 40 p.s.i.g. Immediately upon reaching 40 p.s.i.g. in the autoclave, the saturated steam introduction was stopped and the autoclave was vented to the atmosphere in order to reduce the pressure therein to atmospheric as quickly as possible. Thereafter, the above procedure or cycle was repeated 4 times with the exception that evacuation of the autoclave was eliminated between cycles. The staple fiber was then removed from the autoclave and dried. The staple fiber thus treated was carded on a standard cotton carding machine and spun into yarn in conventional manner. The yarn was then employed in making a tricot knit tape, as outlined hereinbefore and the tape was designated as sample B.

A standard sample A was also prepared from the filaments of this example by cutting into staple fibers, carding, spinning into yarn and making a tricot knit tape from said yarn in the same manner as sample B. The standard sample A was not annealed as described in connection with sample Comparative data was obtained and the same is tabulated below:

1 Percent breakdown indicates the percent of the total fibers carded which have a shorter fiber length after cardlng than the fiber length before carding.

2 S.E.P. means Single End Product and it IS the numeriealfignre used to express single and strength and it is obtained by multiplying the strength of the strand in ounces by the yarn number.

In the above table, S.E.P. and elongation were determined using a 30 singles yarn whereas TR was obtained on a 16 singles yarn, as hereinbefore pointed out. It can readily be seen, from the above data, that fibers produced in accordance with the present invention are not only substantially non-fibrillating, but they have increased strength and elasticity and exhibit greatly improved performance on the card. Performance during carding is extremely important since a fiber which cannot be carded satisfactorily cannot be formed or spun into a commercially suitable yarn. The percent breakdown is an indication of whether a particular fiber will spin into a satisfactory yarn.

EXAMPLE II The same procedure as outlined in Example I was followed here using a copolymer containing 94% by weight in the polymer molecule of acrylonitrile and 6% by weight of vinyl acetate. After cutting the dried filaments into staple fibers, one hundred (100) pounds of the fibers were placed in a perforated metal container which in turn was placed in an autoclave. The autoclave was evacuated and saturated steam, at approximately 40 p.s.i.g., introduced therein until the pressure in the autoclave reached 40 p.s.i.g. Upon reaching said pressure, steam introduction was stopped and the autoclave vented to the atmosphere. Thereafter, the above procedure was repeated 3 times with the exception that evacuation of the autoclave was eliminated between cycles. Thereafter the staple fiber was treated as outlined in Example I and the tape was designated as sample D. A standard sample C was also prepared with the exception that it was not annealed, as described in connection with sample D. Comparative data was obtained and the same is tabulated below:

Table 2 Sample D (Annealed) Unable to sp .do 2.6

In the above table, S.E.P. and elongation were determined using a 30 singles yarn whereas TR was obtained on a 16 singles yarn. It is significant to note that in the case of sample C, or unannealed, it was not possible to spin a 30 singles yarn and accordingly, no data on S.E.P. and elongation was obtainable. It was not possible to spin the smaller 30 singles yarn because of the broken or shorter fibers, which in turn resulted from highbreakdown during carding. No such difficulty was encountered in processing the annealed sample D.

It will be readily apparent that the present invention is the answer to and overcomes the deleterious fibrillation problem. In addition, other beneficial results and advantages accrue from the practice of the instant invention. When dyed fabrics are made from fibers and filaments of the instant invention, they show no color change on ironing. In addition, it has unexpectedly been found that structures produced by the present invention show increased dyeability over structures produced from acrylonitrile polymers by other known techniques. Further, when spinning fibers and filaments into yarn in textile mills, fly or lint presents a problem. It has been found that filaments and fibers, produced in accordance with the present invention produce less fly in the textile mills, when processed into yarns and threads, than filaments and fibers produced by prior art procedures. Numerous other advantages of the present invention will be apparent to those skilled in the art.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A process for producing substantially non-fibrillating filaments comprised of a material selected from the group consisting of acrylonitrile polymers containing at least 70 percent of acrylonitrile and up to 30 percent of other polymerizable mono-olefinic monomers copolymerizable .therewith and blends of said polymers with a polymer of an alkenyl-substituted N-heterocyclic compound, said blends containing from 50 to 80 percent by weight of acrylonitrile, which comprises placing said filaments in a closed chamber while in an oriented and crystalline state, evacuating said chamber, introducing wet steam into said chamber at a pressure in the range of 30 to 60 p.s.i.g. and a temperature in the range of 135 to 155 C. until the pressure in said chamber is in the range of 30 to 60 p.s.i.g., and thereafter immediately venting the chamber to the atmosphere, said process being repeated until the filaments are substantially non-fibrillating.

2. The process as defined in claim 1 wherein after venting the chamber to the atmosphere the chamber is evacuated to cool the filaments and to remove excess water therefrom.

3. The process as defined in claim 1 wherein the filaments are comprised of an acrylonitrile polymer containing at least 70 percent of acrylonitrile and up to 30 percent of other polymerizable mono-olefinic monomers copolymerizable therewith.

4. The process as defined in claim 1 wherein the filaments are comprised of polyacrylonitrile homopolymer.

5. The process as defined in claim 1 wherein the filaments are comprised of a blend of (A), a copolymer containing 94 percent by weight in the polymer molecule of acrylonitrile and 6 percent of vinyl acetate and (B), a copolymer containing 50 percent by weight of acrylonitrile and 50 percent by Weight of a vinylpyridine, said copolymer (B) being employed in sufiicient amount to give 3 to 8 percent by weight of the vinylpyridine, based on the Weight of the blend.

6. The process as defined in claim 1 wherein the filaments are comprised of a copolymer of 94 percent by weight in the polymer molecule of acrylonitrile and 6 percent by weight of vinyl acetate.

7. Filaments produced in accordance with the process of claim 1 which are substantially non-fibrillating and have a tricot rating not greater than 2.0.

. ments are comprised of a blend of (A) a copolymer containing 90 to 98 percent by weight in the polymer molecule of acrylonitrile and 2 to 10 percent of vinyl acetate and (B) a copolymer of 10 to percent by Weight in the polymer molecule of acrylonitrile and 30 to percent of 2-methyl-5-vinylpyridine, said copolymer (B) be ing employed in sufficient amount to give 3 to 8 percent by Weight of 2-methyl-5-vinylpyridine, based on the Weight of the blend.

12. A process for producing substantially non-fibrillating filaments comprised of a material selected from the group consisting of acrylonitrile polymers containing at least 70 percent of acrylonitrile and up to 30 percent of other polymerizable mono-olefinic monomers copolymerizable therewith and blends of said polymers with a polymer of an alkenyl-substituted N-heterocyclic compound, said blends containing from 50 to 80 percent by weight of acrylonitrile which comprises placing said filaments in a closed chamber while in an oriented and crystalline state, evacuating said chamber, introducing wet steam into the chamber at a pressure in the range of 30 to 60 p.s.i.g. and a temperature in the range of to C. until the pressure in the chamber is in the range of 30 to 60 p.s.i.g., immediately venting the chamber to the atmosphere to reduce the pressure therein to approximately 2 p.s.i.g., thereafter repeating said process until the filaments are substantially non-fibrillating, and evacuating the chamber to cool the fibers and remove excess moisture therefrom.

13. The process as defined in claim 12 wherein the filaments are comprised of a blend of (A), a copolymer containing 94 percent by weight in the polymer molecule of acrylonitrile and 6 percent of vinyl acetate and (B), a copolymer containing 50 percent by weight of acrylonitrile and 50 percent by weight of a vinylpyridine, said copolymer (B) being employed in sufficient amount to give 3 to 8 percent by weight of the vinylpyridine, based on the weight of the blend.

14. The process as defined in claim 12 wherein the filaments are comprised of a copolymer of 94 percent by weight in the polymer molecule of acrylonitrile and 6 percent by weight of vinyl acetate.

References Cited in the file of this patent UNITED STATES PATENTS 2 ,185,789 Jacque Jan. 2, 1940 2,373,093 Baker Apr. 10, 1945 OTHER REFERENCES Du Pont: Textile Fibers Tech. Inf0r., Bull. OR-67, August 1955.

Textile Res. Jour., July 1954, pp. 597-603. 

1. A PROCESS FOR PRODUCING SUBSTANTIALLY NON-FIBRILLATING FILAMENTS COMPRISES OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ACRYLONITRILE POLYMERS CONTAINING AT LEAST 70 PERCENT OF ACRYLONITRILE AND UP TO 30 PERCENT OF OTHER POLYMERIZABLE MONO-OLEFINIC MONOMERS COPOLYMERIZABLE THEREWITH THE BLENDS OF SAID POLYMERS WITH A POLYMER OF AN ALKENY-SUBSTITUTED N-HETEROCYCLIC COMPOUND, SAID BLENDS CONTAINING FROM 50 TO 80 PERCENT BY WEIGHT OF ACRYLONITRILE, WHICH COMPRISES PLACING SAID FILAMENTS IN A CLOSED CHAMBER WHILE IN AN ORIENTED AND CRYSTALLINE STATE, EVACUATING SAID CHAMBER, INTRODUCING WET STEAM INTO SAID CHAMBER AT A PRESSURE IN THE RANGE OF 30 TO 60 P.S.I.G. AND A TEMPERATURE IN THE RANGE OF 135* TO 155*C. UNTIL THE PRESSURE IN SAID CHAMBER IS IN THE RANGE OF 30 TO 60 P.S.I.G., AND THEREAFTER IMMEDIATELY VENTING THE CHAMBER TO THE ATMOSPHERE, SAID PROCESS BEING REPEATED UNTIL THE FILAMENTS ARE SUBSTANTIALLY NON-FIBRILLATING. 